1. Technical Field
The present invention relates to a light scanning apparatus and a separation distance measurement apparatus.
2. Related Art
Existing light scanning apparatuses for scanning a light beam in a specific direction are employed in various fields, including in image forming apparatuses such as laser printers, and separation distance measurement apparatuses such as laser radar apparatuses. There is, for example, a proposal for a reflection measurement apparatus employed for vehicle separation distance control that performs two dimensional scanning using a rotating multifaceted mirror equipped with plural reflecting surfaces of differing tilt angles, and for a vehicle separation distance control apparatus employing such as reflection measurement apparatus (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 9-274076). In the apparatus of JP-A No. 9-274076, a laser beam is illuminate from obliquely above a inclined reflecting surface of a rotating multifaceted mirror, and plural beams reflected by respective reflecting surfaces are scanned.
However, when two dimensionally scanning emission beams using a rotating multifaceted mirror equipped with inclined reflecting surfaces as described in JP-A No. 9-274076, the scanning angle range in the vertical direction (called the “elevation angle”) within a vertical flat plane orthogonal to the center of the measurement area differs at the two ends of the measurement area, generating distortion in the trapezoidal measurement area, called “vertical distortion”. In the apparatus of JP-A No. 9-274076, the laser beam is caused to be incident on the tilted reflecting surface from obliquely above, and vertical distortion is only reduced in a narrow range of bearing angles of 20° or less.